R Plotly show string on contour plots - r

Question

I have overlayed two contour plots:
library(plotly)
cluster_count <- 5
volcan <- plot_ly(z = ~volcano,
type = "contour",
contours = list(
coloring= "fill",
showlines = F
))
cluster_matrix <- volcano
cluster_matrix[cluster_matrix < 100] <- 1
cluster_matrix[cluster_matrix <= 120 & cluster_matrix >= 100] <- 2
cluster_matrix[cluster_matrix < 140 & cluster_matrix >= 120] <- 3
cluster_matrix[cluster_matrix <= 160 & cluster_matrix >= 140] <- 4
cluster_matrix[cluster_matrix > 160] <- 5
cluster_name_matrix <- cluster_matrix
cluster_name_matrix[cluster_matrix ==1] <- "Eins"
cluster_name_matrix[cluster_matrix ==2] <- "Zwei"
cluster_name_matrix[cluster_matrix ==3] <- "Drei"
cluster_name_matrix[cluster_matrix ==4] <- "Vier"
cluster_name_matrix[cluster_matrix ==5] <- "Funf"
volcan %>% add_contour(cluster_matrix,
type = "contour",
opacity =1,
text=cluster_name_matrix,
hovertemplate = 'Cluster: %{text}<extra></extra>',
autocontour = F,
line=list(color="orange"),
contours = list(
start = 1,
showlabels = T,
coloring= "lines",
end = cluster_count,
size = 1,
showlines = T
))
Is it possible to have a plot like this:
Like I did for the hovering text? Thanks for tips and suggestions in advance!

Answer 1

What you've been looking for is the add_annotations() function. In the code below, I write a function that retrieves a random coordinate pair for each level and then passes the corresponding coordinates to the add_annotations() function. Note that I stored your contour plot in the variable p:
library(purrr)
# Custom function
find_rand_annotation_index <- function(name_matrix, string){
d <- which(name_matrix == string, arr.ind = TRUE)
d2 <- as.data.frame(d[sample(nrow(d), size = 1), , drop = FALSE])
cbind(d2, string)
}
# Get 5 random coordinates to plot the labels
text_coords <- purrr::map_dfr(c("Eins", "Zwei", "Drei", "Vier", "Funf"), ~ find_rand_annotation_index(cluster_name_matrix, .x))
# Plot the annotations on the contour plot
p %>%
add_annotations(
x = text_coords$col,
y = text_coords$row,
text = text_coords$string,
font = list(color = "IndianRed"),
showarrow = F
)
The positioning of the labels may not be to your liking (because the coordinates are chosen randomly), but you may want to do something about it in your code.